I was having a problem. When I open the app before my splash screen loads a black screen was appearing. I found that the reason for this black screen is that on app launch, Android displays a simple preview window (based on your activity theme) as an immediate response to the user action. Then the preview window crossfades with the actual UI, once that has fully loaded .
I could not find a "nice" way to get rid of this black preview window. This is the only solution I found.
1. Go to AndroidManifest.xml inside the path_to_sencha_cmd/Sencha/Cmd/126.96.36.199/stbuild/st-res/android/
(I was using the version 188.8.131.52. The path depends on that.)
2. Inside application tag change the theme as android:theme="@android:style/Theme.Light"
If you do not want the title bar use this instead of the above one.
I don't think this is a good way to solve the problem. But I could not find a better way rather than changing Sencha cmd code.